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CHARACTERISTICS OF LIGHTWEIGHT CONCRETE FILLED WITH PALM-BASED
POLYURETHANE
KAMARUL AINI MOHD SARIa*
, SOHIF MATa, KHAIRIAH HAJI BADRI
b,
MUHAMMAD FAUZI MOHD ZAINc
*Universiti Tun Hussein Onn Malaysia, 86400 Batu Pahat, Johor, Malaysia
aSolar Energy Research Institute
bPolymer Research Center, Faculty of Science and Technology
cFaculty of Engineering and Built Environment
Universiti Kebangsaan Malaysia 43600 UKM Bangi, Selangor, Malaysia.
[email protected], [email protected], [email protected], [email protected]
www.ukm.my/seri
Abstract: Several experiments were conducted to characterize the properties of palm-based polyurethane (PU)
foam in lightweight concrete. The PU foam was synthesized from palm kernel oil-based polyol reacted with 2,
4-methylene diphenyl diisocyanate. Polyurethane foam with size of 5 mm was mixed with ordinary Portland
cement, sand, and water to form lightweight concrete. The microstructure of PU aggregate can be assessed
from optical micrographs. Density, compressive strength, distribution of fine aggregate, and the interfacial zone
were also investigated. The result showed that palm-based lightweight concrete has excellent compressive
strength (17 MPa), and fulfilled the minimum strength requirement for structural concrete. Palm-based light-
weight concrete with 0.6 w/c ratio and 3% w/w PU achieved 1770 kg/m3 presented uniform dispersion of ag-
gregate and excellent mechanical bonding.
Key-Words: polyurethane, palm kernel oil, lightweight concrete, compressive strength, interfacial zone
1 Introduction Lightweight concrete can be produced by introduc-
ing lightweight aggregate, such as expanded clay,
expanded polystyrene, polyurethane, and so on
[1,2]. Within the wide range of plastics materials,
the manufacture of polyurethane (PU) by polyiso-
cyanate/ polyol reaction occupies a special place
because of its broad spectrum of applications. The
properties of high molecular polyurethane products
can be controlled chemically and physically in such
a manner that different properties are achieved. In
general, most polyols used in the polyurethane in-
dustry are petroleum-based, where crude oil and
coal are used as starting raw materials. However, the
prices of these polyols are high because of the high
technology processing system.
This study presents the usage of a natural
material, palm kernel oil polyol (PKO-p), as a sub-
stitute in the polyurethane industry. Badri and co-
workers [3] had successfully produced and devel-
oped polyurethane for wide applications, such as
rigid foam, elastomer, coating, adhesive, and seal-
ant. Usage of PU polyol in the making of concrete
has not been reported elsewhere. The PU systems
consist of PKO-p and 2, 4-methylene diphenyl
diisocyanate (crude MDI). The molecular weight
and the functionality of polyols affect the resulting
foam properties. Polyisocyanates act as the jointing
agent of polyols. Therefore, urethane and related
foams are recognized as building block polymers
[4].
In the meantime, the palm-based light-
weight concrete for this study exclusively considers
structural lightweight concrete, that is a mixture of
ordinary Portland cement, fine sand, water, and
polyurethane particles, as fine aggregates less than 5
mm [5,6]. Normal weight concrete mixes typically
have densities above 2400 kg/m3, whereas light-
weight concrete (LWC) has a density ranging from
800 kg/m3
to 1800 kg/m3. Structural lightweight
concrete commonly has a 28-day compression
strength comparable to normal weight concrete
[7,8].
In the present study, an attempt was made to
examine the development and formulation of poly-
urethane and lightweight concrete. The density,
compressive strength, and the interfacial zone
within the hardened cement paste using optical mi-
crographs were investigated.
2 Experimental Procedure PKO-polyol and MDI were mixed using an over-
head stirrer at a speed of 1000 rpm for 10 s to form
the polyurethane system. The mixture was then
poured into a screw-tight mold, and was allowed to
cure for 10 min. Rigid PU foam was demolded and
conditioned at room temperature for 16 h prior to
characterizations. The ratio of PKO-p resin to MDI
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was fixed to 1:1. PU system which function
lightweight aggregate in concrete was gr
sieved to a size of 5 mm.
An attempt to identify the formulation of
palm-based lightweight concrete less than 1800
kg/m3 was conducted. Notably, the most effective
and dominant parameters that affect density and
compressive strength are loading percentage
and water per cement (w/c) ratio [9].
loading percentage of PU system and w/c ratio
set as varying variables. The optimization study i
dicated that 0.6 w/c ratio with 3% (w/w)
were optimum ratio and processing composition
Palm-based lightweight concrete was prepared by
integrating cement, sand, and w/c
1:2:0.6 in a drum mixer. About 3% (w/w) of PU
system with size of 1 mm to 5 mm were mix
the concrete mixture for another 3 min until un
formly distributed. The specimens were cast
steel mold of 100 mm × 100 mm × 100 mm
sions. The density and compressive strength
determined.
3 Characteristics Density of PU rigid foam (kg/m
3) was
following BS4370: Part 1: 1988 Method 2
culated using the equation of mass (
volume (m3). The PU was prepared by molding
technique into a cubic mold of 50 mm
50 mm in dimensions. Three replicates
fully weighed using an analytical balance
mass was recorded.
The density of the lightweight concrete
calculated using equation (1)
EN12390: Part 7: 2002 standard. The s
were prepared by molding technique into
mold of 100 mm × 100 mm × 100 mm in dime
sions. Three replicates were carefully weighed using
an analytical balance and the mass was recorded.
The density was measured and calculated
lows:
v
m ρ = (1)
ρ = density (kg/m3)
m = mass (kg)
v = volume (m3)
Compressive strength test was
according to BS EN 12390: Part 3: 2001 standard.
The test was carried out using Autocon 2000
versal Testing Machine with a loading rate 7.0
The specimens were prepared by molding technique
functioned as the
was grind and
An attempt to identify the formulation of
based lightweight concrete less than 1800
the most effective
affect density and
loading percentage of PU
and water per cement (w/c) ratio [9]. Therefore,
PU system and w/c ratio were
optimization study in-
(w/w) PU system
sing composition.
based lightweight concrete was prepared by
at a ratio of
3% (w/w) of PU
1 mm to 5 mm were mixed into
the concrete mixture for another 3 min until uni-
formly distributed. The specimens were casted in a
100 mm dimen-
he density and compressive strength were
was determined
Method 2 and cal-
(kg) divided by
prepared by molding
50 mm × 50 mm ×
replicates were care-
fully weighed using an analytical balance and the
of the lightweight concrete was
following BS
The specimens
prepared by molding technique into a cubic
100 mm in dimen-
were carefully weighed using
and the mass was recorded.
calculated as fol-
(1)
was conducted
according to BS EN 12390: Part 3: 2001 standard.
The test was carried out using Autocon 2000 Uni-
loading rate 7.0 kN/s.
pecimens were prepared by molding technique
into a cubic mold of 100 mm
in dimensions. They were
time of 7, 14, and 28-days
and load peak data were recorded. The compressive
strength was calculated using equation (2). Fig.
shows the test setup to determine
strength of the concrete cube.
f c =
fc = compressive strength
F = maximum load
A = area (m2)
Fig.1 Setup apparatus for the compressive strength
of palm based lightweight concrete
The optical micrograph analysis
out to study the dispersion and interfacial
between PU systems and cement paste. The analysis
was carried out using a Dino
model AM-413T. The dried samples were cut and
scanned at 500× magnifications.
4 Result and DiscussionPolyurethane is produced through the reaction
between polyhydroxyl compound (polyol
diisocyanates (crude MDI)
equation below :
Polyurethanes are block copolymers co
taining segments of low molecular weight polyester
or polyether bonded to a urethane group (
O) [11]. Generally, a polyether or polyester
produce soft segments, whereas
bond will form hard segments
tion was carried out effectively through the control
of carbon dioxide gas emissions in a polymerization
system. Polyurethane is formed through the ex
thermic reaction between the compounds containing
mm × 100 mm × 100 mm
They were tested based on exposure
s. The compressive stress
and load peak data were recorded. The compressive
ulated using equation (2). Fig.1
setup to determine the compressive
concrete cube.
A
F (2)
compressive strength (MPa)
load at failure (N)
for the compressive strength
of palm based lightweight concrete
The optical micrograph analysis was carried
to study the dispersion and interfacial adhesion
between PU systems and cement paste. The analysis
was carried out using a Dino-lite Microscope Pro
413T. The dried samples were cut and
magnifications.
Result and Discussion Polyurethane is produced through the reaction
polyhydroxyl compound (polyol) and
MDI) [10] as shown in the
Polyurethanes are block copolymers con-
taining segments of low molecular weight polyester
or polyether bonded to a urethane group (-NHCO-
a polyether or polyester will
ereas MDI in the urethane
bond will form hard segments. Polyurethane forma-
carried out effectively through the control
emissions in a polymerization
Polyurethane is formed through the exo-
thermic reaction between the compounds containing
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isocyanate (-NCO) and functional groups with ac-
tive hydrogen (-XH).
4.1 Density From the experiment, PU obtained was categorized
as high-density rigid PU with density ranging from
196 kg/m3
to 409 kg/m3. Excess PKO-p increased
the strength with the highest compressive strength at
11.4 MPa. The compression strength of the PU in-
creased with increasing density but somehow affect
the thermal conductivity of the lightweight concrete
[5,12]. Therefore, in this study, 1:1 ratio of the
PKO-p to MDI with a density of 206 kg/m3 was set
as the lightweight aggregate.
Fig.2 shows the effects of palm-based PU
on the lightweight concrete density with various w/c
ratios of the concrete mix. The investigated w/c ra-
tios were 0.5, 0.6, and 0.7 with 0% to 5% (w/w)
percentage loading of PU. This resulted in density
of approximately 1200 kg/m3
to 1850 kg/m3. By in-
creasing the volume of PU system in the concrete
from 1% to 5% (w/w), the density decreased within
the range of 22% to 35%. Lower w/c ratio resulted
in lower density sample, which consequently result
in a dehydrated mixture and low workability. On the
other hand, increasing the amount of PU system also
dehydrated the mixtures and weakened the interac-
tion between PU and the mortar. To resolve the fac-
tors which influence the compressive strength and
thermal conductivity, the w/c ratio is optimized to
obtain a mixture with good workability [5,12,13]. At
0.6 w/c ratios and 3% (w/w) of PU is able to pro-
duce a homogeneous, highly workable, and easy-to
cast lightweight concrete.
Fig.2 The effects of palm-based PU addition on
the lightweight concrete density with various w/c
ratios of the concrete mix.
Needless to say that common practice applies 0.5
w/c ratio which is much depending on lightweight
concrete manufacture. David et al. [7,14] stated that
in terms of the water retained in the pores of the ag-
gregate, most lightweight concretes retain, absorb,
and release considerably more water than normal
weight aggregates.
4.2 Compressive strength The compressive strength of the PU system with
excess PKO-p and with additional MDI is from 7.0
MPa to 11.5 MPa and from 7.0 MPa to 4.4 MPa,
respectively. The compressive strength increased
with additional of PKO-p. The compressive strength
of PU system with 1:1 ratio was 7.0 MPa.
Fig.3 shows the compressive strength of control
and palm-based lightweight concrete. At 7 and 28
days, lightweight concrete with 3% PU range from
11.3 MPa to 17.5 MPa. The graph indicates that
compressive strength is a function of time. The
strength increased upon prolongs exposure and
gradually increased after 28 days to approximately
54%.
Fig.3 Effect of varying PU addition in the
lightweight concrete on the compressive strength
Apparently, the strength of this concrete is
sufficient to make it a structural concrete in accor-
dance to the minimum strength requirement. ACI
213R-8 Guide for Structural Lightweight Aggregate
Concrete defines structural lightweight aggregate
concrete as those having a 28-day compressive
strength of more than 17 MPa and air-dried weight
not exceeding 1850 kg/m3.
Fig. 4 exhibits the cracks appeared on the con-
crete cubes undergone compression test. The length
of the crack propagation dispersed to all direction.
The failure mode of this concrete indicated that PU
lightweight aggregate concrete experienced failure
spread in all directions. It is categorized as a satis-
factory failure following the standards. The stress
transfer is prominently to all samples containing PU.
1000
1200
1400
1600
1800
2000
2200
C 1 2 3 4 5
De
nsity (
kg
/m3
)
Amount of PU aggregate, % (w/w)
0.5 w/c0.6 w/c0.7 w/c
0
5
10
15
20
25
30
7 14 28Co
mp
ress
ive
str
en
gth
(M
Pa
)
Exposure Time, days
control LWC (0% PU)
LWC with 3.0% PU
LWC with 3.5% PU
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Fig.4 Concrete cubes undergone compression test
4.3 Distribution of aggregate and
Micrograph By visual observation, PU without any
ing agents or admixtures apparently showed an even
distribution in the mortar and concrete matrix
shown in Fig.5. The broken fragment showed that
cement paste occupied all voids and open pore
PU in contact zone. Meanwhile, PU also filled up
voids in the concrete system. In general, palm
lightweight concrete showed good workability and
could be easily compacted and turned to
products.
Fig.5 PU covered by cement paste in the broken
fragment of concrete.
Fig.6 Interfacial zones between concrete and PU
observed using optical microscope at
cations.
The interfacial zones of palm
lightweight concrete with PU was observed
compression test
Distribution of aggregate and Optical
any special bond-
ing agents or admixtures apparently showed an even
distribution in the mortar and concrete matrix, as
5. The broken fragment showed that
occupied all voids and open pores of
in contact zone. Meanwhile, PU also filled up
system. In general, palm-based
lightweight concrete showed good workability and
turned to finished
covered by cement paste in the broken
between concrete and PU
at 500× magnifi-
nterfacial zones of palm-based
with PU was observed using
optical microscope and presented
ical bonding completely interlocked
The well-built bonding between
the mortar is attributable to the fact that
not rounded in shape and has a
kar et al. [15] stated that the mechanical bond b
tween the aggregate surface and
by virtue of interlocking, influences the strength of
concrete.
5 Conclusion The mix proportion of palm
sity, γ = 1770 kg/m3) concrete filled with PU system
meets the requirement for structural concrete (co
pressive strength, fc = 17 MPa) as below:
i) PU system (PKO
ii) Mortar (cement to sand is 1:2).
iii) Water per cement ratio is 0.6.
Based on the observation
crographs, the morphology
concrete indicated excellence
zone. The mechanical bonding between
gate and the cement paste was completely inte
locked to each other and the
zone is generally stronger
strength of palm based lightweight concrete i
creased with increasing strength and density of the
PU.
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[1] Satish Chandra,
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) concrete filled with PU system
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= 17 MPa) as below:
PU system (PKO-P to MDI is 1:1 ratio).
Mortar (cement to sand is 1:2).
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